{
  "circularId": 41277,
  "version": 2,
  "body": "EP250807a: EP-WXT detection of a fast X-ray transient\n\nY. Wang (PMO, CAS), Y. Q. Zhao (USTC,PRIC), H. Q. Cheng, Z. X. Ling (NAOC) on behalf of the Einstein Probe (EP) team:\n\nWe report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP250807a. The transient triggered EP-WXT (ID: 06800000803) at 2025-08-07T23:33:02 (UTC). The WXT position of the source is R.A. = 281.311 deg, DEC = 14.383 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). The duration of the flare is about 250 seconds, with a peak flux of 2.08 x 10^-8 ergs/s/cm^2. The WXT spectrum during the flare can be fitted with an absorbed power-law model, yielding best-fit absorption column density of 0.80 (-0.26, +0.27) x 10^22 cm^-2 and photon index of 1.99 (-0.11, +0.14). The 0.5-4 keV unabsorbed flux is 7.14 (-1.59, +2.71) x 10^-9 ergs/s/cm^2.\n Follow-up observations with several optical telescopes (Globus et al., GCN 41275; Kumar et al., GCN 41276) yielded only upper limits.\n\nFollow-up observations with EP-FXT are scheduled.\n\nLaunched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).\n\n",
  "createdOn": 1754638090699,
  "submitter": "EP Team at NAOC/CAS <ep_ta@bao.ac.cn>",
  "subject": "EP250807a: EP-WXT detection of a fast X-ray transient",
  "editedBy": "Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of EP Team at NAOC/CAS <ep_ta@bao.ac.cn>",
  "bibcode": "2025GCN.41277....1W",
  "editedOn": 1754662288141,
  "eventId": "EP250807a",
  "submittedHow": "web",
  "format": "text/plain"
}